Negative electrode for lithium ion secondary battery, and lithium ion secondary battery using the same

Abstract

A negative electrode for a lithium ion secondary battery, which has high energy density and which can suppress a crease (form change) of a negative electrode active material layer and a negative electrode current collector caused by the expansion and contraction occurring along with the quick charging and discharging and also suppress the falloff of the negative electrode active material layer after the quick charging and discharging cycle, and a lithium ion secondary battery using the negative electrode. The negative electrode for a lithium ion secondary battery and the lithium ion secondary battery include: a negative electrode active material including 5% or more of silicon or silicon oxide; a binder that is polyacrylate whose carboxylic groups at terminals of side chains of polyacrylic acid are cross-linked with magnesium or alkaline earth metal; and a negative electrode current collector.

The invention claimed is: 
     
       1. A negative electrode for a lithium ion secondary battery, comprising:
 a negative electrode active material including 5 wt % or more of at least one silicon component selected from the group consisting of silicon oxide, elemental silicon, an alloy of silicon, and a compound of silicon other than silicon oxide; 
 a binder that is a polyacrylate obtained by a reaction of a polyacrylic acid and magnesium, an alkaline earth metal, a compound of magnesium, or a compound of an alkaline earth metal, and whose 1% or more of carboxylic groups at terminals of side chains of the polyacrylic acid are cross-linked with magnesium or alkaline earth metal; and 
 a negative electrode current collector. 
 
     
     
       2. The negative electrode for a lithium ion secondary battery according to  claim 1 , wherein a cross-linking degree of the polyacrylate cross-linked with magnesium or alkaline earth metal is 1 to 90% relative to the carboxylic groups included at terminals of side chains of the polyacrylic acid. 
     
     
       3. The negative electrode for a lithium ion secondary battery according to  claim 1 , wherein an average polymerization degree of the cross-linked polyacrylate is 3,000 to 30,000. 
     
     
       4. A lithium ion secondary battery comprising the negative electrode for a lithium ion secondary battery according to  claim 1 . 
     
     
       5. The negative electrode for a lithium ion secondary battery according to  claim 1 , wherein the negative electrode active material comprises elemental silicon. 
     
     
       6. The negative electrode for a lithium ion secondary battery according to  claim 1 , wherein the negative electrode active material comprises silicon oxide. 
     
     
       7. The negative electrode for a lithium ion secondary battery according to  claim 1 , wherein the negative electrode active material comprises a silicon compound selected from the group consisting of SiB 4 , SiB 6 , Mg 2 Si, Ni 2 Si, TiSi 2 , MoSi 2 , NiSi 2 , CaSi 2 , CrSi 2 , Cu 5 Si, FeSi 2 , MnSi 2 , NbSi 2 , TaSi 2 , VSi 2 , WSi 2 , and ZnSi 2 . 
     
     
       8. The negative electrode for a lithium ion secondary battery according to  claim 1 , wherein the total weight of the silicon component in the total weight of the negative electrode active material is 20 wt % or more. 
     
     
       9. The negative electrode for a lithium ion secondary battery according to  claim 1 , wherein the total weight of the silicon component in the total weight of the negative electrode active material is 40 wt % or more. 
     
     
       10. The negative electrode for a lithium ion secondary battery according to  claim 1 , wherein a cross-linking degree of the polyacrylate cross-linked with magnesium or alkaline earth metal is 30 to 90% relative to the carboxylic groups included at terminals of side chains of the polyacrylic acid. 
     
     
       11. The negative electrode for a lithium ion secondary battery according to  claim 1 , wherein an average polymerization degree of the cross-linked polyacrylate is 6,500 to 30,000. 
     
     
       12. The negative electrode for a lithium ion secondary battery according to  claim 1 , wherein an average polymerization degree of the cross-linked polyacrylate is 3,000 to 11,000.